In the mass production of baked goods such as crackers, cookies and snacks using a continuous baking process, dough pieces are subjected to heating in a plurality of temperature zones to leaven the dough pieces, reduce their moisture content, and develop flavor, color, shape, and textural attributes such as crispness, crunchiness, and tenderness. The final moisture content of the product exiting the oven affects its shelf-life and texture. The baking process should provide a consistent moisture content to assure shelf stability and a desirable texture.
However, in gas-fired continuous baking ovens variation in heating generally occurs across the width of the oven band, which may be up to about five feet in width. Lower and higher temperatures can be established at various points on the oven band due to variable conditions primarily related to corrective air flow patterns and radiative effects. Changes in ambient air temperature, gas pressure, dough weights, and dough moisture content from batch to batch may also result in excessive variations in baked product moisture content in pieces across the band as well as along its length, which may be up to about 300 feet. Non-uniform distribution of heat may occur along the length of the oven, with the development of hot zones on the band adjacent each burner and cooler spots midway between adjacent burners. Baked products with moisture contents out of a specified range are either discarded or recycled, thereby resulting in loss of efficiency and increased costs.
The variations in heating across the width of the oven band and along its length can also lead to undesirable, substantial variations in the amount of leavening or oven rise from piece to piece. Baked piece height variation, if excessive, adversely affects the attainment of a consistent stack height. In packaging systems, such as for slug-type packaging, where baked pieces are packaged or stacked face-to-face if the stack height for a given number of pieces is too low, an extra piece needs to be added to the stack, thereby resulting in increased weight and production costs. Inversely, if the stack height for a given number of baked pieces is too high, the slug or even a dump-fill bag may not contain a sufficient number of pieces to meet the package label weight requirement.
Upon detection of baked product moisture contents and stack heights which do not meet specifications, heat inputs into one or more zones of a gas fired oven may be adjusted along with exhaust extraction rate to control chamber humidity to bring the baked product back into specifications. However, the adjustment time or response time to bring the moisture content or stack height back into specifications generally takes at least about an hour. Since the oven is a continuous oven, the longer it takes to make the adjustment, the more product produced out of specifications and the greater the amount of out-of-specification product. The prolonged adjustment time is generally due to the time needed for manual adjustment of the gas burners, and for the massive ovens to cool down or heat up and reach a steady state. Additionally, variations across the oven band width generally can not be readily, substantially reduced. Furthermore, gas burner flow rate adjustments to change the moisture content may adversely affect stack height, and vice versa.
As disclosed in U.S. Pat. No. 5,369,250 to Meredith, microwave heating ovens are well-known for the rapid volumetric heating of food. However, a common problem encountered with the microwave heating is the lack of uniformity of heating particularly on the edges and corners of solids. A microwave heating device having a microwave emission slot is used to achieve substantially uniform heat distribution, and for controlling the rate of rise of temperature in an article without unnecessary energy loss between articles in a train of articles.
The rapid heating provided by microwaves has been used to reduce baking times in the production of bread as disclosed in U.S. Pat. No. 5,290,575 to Torikata and U.S. Pat. No. 5,334,402 to Ovadia. or increase oven throughput. Additional heating means, it is disclosed are needed to obtain browning of the bread.
Continuous mixing of cake-making components to form a gas-infused batter, and thereafter expanding and cooking the batter under the application of microwave energy to form a baked sponge cake is disclosed in U.S. Pat. No. 4,350,713 to Dyson et al. The continuous process, it is disclosed does not require a long leavening time.
U.S. Pat. Nos. 3,630,755 and 3,699,899 each to Schiffmann et al discloses the use of microwave energy to reduce proofing time in the production of yeast-raised bakery products such as yeast-raised doughnuts. The dough pieces are subjected to at least two microwave heating periods separated by a "rest" period. The initial microwave heating of the dough rapidly raises its temperature to a level at which appreciable gassing of the yeast can take place. During the second interval, when the microwave power is turned off, the dough is maintained at a temperature at which relatively fast gassing can take place. During this "rest" interval, the temperature of the dough equilibrates. A widely varying temperature within any dough piece, it is disclosed, would give rise to a non-uniform density of the finished product. The different parts of the dough piece would expand to different extents during the subsequent heating of the dough piece in the last phase of the proofing process and during frying. During the second microwave interval, the dough temperature rises rapidly to the final proofing temperature. After complete proofing, frying or baking can begin immediately.
U.S. Pat. No. 5,457,303 and International Patent Publication No. WO94/26078 (published Nov.10, 1994) each to Shute et al disclose a combined oven where microwave energy is injected into an oven at various positions along the oven length. The microwave heating, it is disclosed, provides means to induce a rapid transfer of energy to the product, the level of energy transfer being selected to provide a desired effect within the product. In a proposed combined microwave-biscuit oven having four microwave zones, the first microwave zone induces a rapid rise in temperature within the product, the second microwave zone enhances development, and the third and fourth microwave zones reduce the moisture content of the product prior to leaving the oven. Adjusting stack height and moisture content to within product specifications using the microwave energy is not disclosed.
United Kingdom patent publication no. 1,409,227 (published Oct. 8, 1975) discloses the production of bread using a microwave preheating and proofing chamber for partially proofing unproofed dough product. A conventional proofing chamber receives the dough from the preheating chamber for completely proofing the dough. A microwave dough cooking chamber is used to cook the proofed product. A conventionally heated browning zone is used for browning the bread after it has been cooked. Measuring stack height or moisture content of the baked products and adjusting the microwave energy input to control stack height or moisture content is not disclosed.
United Kingdom patent publication no. 1,471,016 (published Apr. 21, 1977) discloses a bakers' oven for baking biscuits in which the dough is passed through at least three separate baking stages, where ambient heat and optionally radiant heat is applied in a first heating section to build the products substantially to a desired thickness and internal structure. An intermediate section having means for subsequently applying high frequency dielectric heating is used for rapidly reducing the moisture content of the products to a substantially constant level for all of the products. A third heating section having means for then applying further ambient heat is employed to impart the desired color and texture to the products. A sensor for detecting the product thickness is provided in the first section and heating adjustments are made therein. A sensor for detecting infra-red radiation or product color is provided in the third section, and radiant energy adjustments may be performed if the dielectric energy fails. Measuring stack height or moisture content of the baked products and adjusting the microwave energy input to control stack height or moisture content is not disclosed.
In a paper presented at a BCCA, United Kingdom Conference in February 1993, "Continuous Production Using Microwaves--Part 2, J. R. Stamper it is disclosed that the use of microwaves in a conventionally heated traveling oven substantially reduces baking times and increases average stack height. However, it is reported that the samples of the biscuits produced in each of the tests were overall poor examples of biscuits. Also, the use of microwaves to adjust stack height so that it is substantially uniform is not disclosed.
It has found that excessive application of microwave energy to remove moisture from a dough and leaven it or to reduce baking time can excessively case-harden the dough and prevent sufficient moisture removal for a shelf-stable product. Discoloration, burning, scorching, and undesirable blistering of the product can result from excessive case-hardening. In addition, in microwaving sheeted doughs, if the dough thickness or height is too low, the microwave energy absorbing ability of the dough may be too low for effective moisture reduction and leavening by microwave treatment.
The present invention provides stack height and moisture content control using microwave energy in the continuous, mass production of baked goods, such as those produced from a dough sheet, without adversely affecting product attributes such as color, texture, shelf stability, weight, and topography. Stack height and product moisture content may be controlled independently of each other. Excessive case hardening which results in product scorching or burning or undesirable blistering are avoided in the processes of the present invention. The response time needed to bring the baked product back into predetermined ranges or specifications for moisture content and stack height is substantially reduced thereby reducing product which is out-of-specifications and reducing recycling. In addition, substantial reductions in gas input into the gas-fired baking ovens may be obtained while achieving substantially evenly leavened products and sufficient moisture reduction to obtain a shelf-stable baked product. The methods may be used for the production of baked goods such as crackers, cookies, sweet and savory snacks The baked goods may be full-fatted, reduced fat, low- fat or no-fat products.